Twitter joined the battle to keep New York's District Attorney out of Occupy protestor Malcolm Harris's tweets on Thursday in what might be a landmark move. As The Atlantic Wire's Adam Martin noted back in February, the New York DA's office subpoenaed "any and all user information, including email address, as well as any and all tweets posted for the period of 9/15/2011-12/31/2011" from Harris' Twitter account. Harris is still fighting a disorderly conduct charge from the big march on the Brooklyn Bridge last year and his motion to quash the subpoena failed two weeks ago. Now, according to the ACLU, Twitter has filed a motion of its own to quash the court order.

This case isn't really about Harris protesting on the Brooklyn Bridge: It's about the limits of privacy on the Internet, and there's hardly any precedent to dictate what a court can and can't do when it comes to user data on sites like Twitter. In the decision against Harris' motion two weeks ago, Judge Matthew Sciarrino Jr. said that "an analogy may be drawn to the bank record cases where courts have consistently held that an individual has no right to challenge a subpoena issued against the third-party bank." Harris's lawyer, Martin Stolar, however, disagrees since tweet data includes a large amount of aggregate information about a person like his location, speech, and interactions with others.

Meanwhile, the American Civil Liberties Union chalks the case up to a violation of Fourth Amendment rights. "This is a big deal," ACLU lawyer Aden Fine said in a blog post. "Law enforcement agencies -- both the federal government and state and city entities -- are becoming increasingly aggressive in their attempts to obtain information about what people are doing on the Internet. And while the individual Internet users can try to defend their rights in the rare circumstances in which they find out about the requests before their information is turned over, that may not be enough."

If the judge denies Twitter's motion, Stolar says there's a good chance it'll end up in a higher court. If that's the case, Stolar and Harris could be standing on shaky ground. Last fall, a federal court ruled that Twitter had to reveal the private data of three WikiLeaks supporters. The court didn't seek a warrant to obtain the data in that case either, but there were larger issues related to WikiLeaks' threat to national security at stake. Twitter stood behind its users in that case, too, and even though it eventually lost, it cemented itself as an advocate for free speech and privacy online. Now, if only the government would do the same.

This article is from the archive of our partner The Wire.

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Adam Clark Estes is a former writer for The Wire. He has also written for The Huffington Postand Vice.